Justin Bieber, 20, is apologising after a video surfaced showing him telling a racist joke five years ago.

In the video obtained by celebrity news website, TMZ, and the UK Sun, the singer says: "Why are black people afraid of chainsaws?"

And then he repeats the punchline, "Run n-----" five times, along with chainsaw noises.

According to The Sun, the video was shot backstage when he was 15 at a promotional event while Bieber was filming his 2011 Never Say Never documentary.

Following the release of the video by the British site and TMZ, Bieber released a statement, saying: "As a young man, I didn't understand the power of certain words and how they can hurt."

"I thought it was ok to repeat hurtful words and jokes, but didn't realise at the time that it wasn't funny and that in fact my actions were continuing the ignorance," he continued.

"Thanks to friends and family I learned from my mistakes and grew up and apologized for those wrongs. Now that these mistakes from the past have become public I need to apologize again to all those I have offended. I'm very sorry."

Oh Biebs, it's just a rollercoaster of ups and downs with you, isn't it?